Joining Element

ABSTRACT

Disclosed is a joining element ( 10 ), especially a suture material for surgical use. The joining element ( 10 ) is composed of a first material ( 12 ) that is essentially rigid during impingement by a relatively short-lasting tensile load on opposite sides as well as a second material ( 11 ) which is connected to the first material. The second material is substantially rigid during impingement by said tensile load on opposite sides while contracting slowly during a second period of time that is longer than the first period of time.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a divisional U.S. patent application Ser. No.11/913,656 filed Jun. 12, 2008, which is a 371 application ofPCT/EP2006/062061 filed May 4, 2006, which claims priority to SwissApplication No. SE 0834/05 filed May 4, 2005, each of which is herebyincorporated by reference in its entirety.

TECHNICAL FIELD OF THE INVENTION

The invention relates to a joining element, especially a suturematerial, especially for surgical purposes, but also relates to atwo-dimensional or three-dimensional textile structure, especially alsofor technical use for joining technical structures, for example.

PRIOR ART

In the event of ligaments or tendons rupturing, a problem that stillremains largely unresolved is that of securing a tendon for example to abone in such a way that the connection does not come loose under theeffect of loading. One of the problems is that the loads that areexerted on a joining element between bone and tendon are very different.Over long periods of time it is desirable for the joining element tocontract, that is to say for the joining element between bone and tendonto tension. It is also possible to have a system with a high degree ofdamping. Movements on the part of the patient may subject the joiningelement to rapidly increasing high loads, under which the connectionmust not fail, which means that, in the event of short-lasting loads onthe tissues connected by the proposed joining element, the healing isnot impaired to a clinically significant extent.

The prior art achieves the connection of different structures (forexample tendon to bone) in the body typically by means of suturematerial, which is rigid and passively transmits the forces that arise.Larger surfaces are bridged (for example in the case of a fascial gap)by means of a two-dimensional load bearer, for example a mesh that isconnectable. Connectable is to be understood as covering a number ofmethods, for example, but not exclusively, suturing, stapling oradhesion.

The use of shape-memory polymers is known, for example, from EP 1 284756, in order to structure muscle, cartilage or nerves in tissueengineering.

In order to bridge more complex defects, planar or three-dimensionalstructures are also of interest (for example a pouch around an organ).An unresolved problem here is how to avoid loosening or tearing of aconnection in the tissue. The invention is intended to remedy thissituation.

Moreover, in the context of securing goods, in particular in the openair, a disadvantage is that textile-based ropes loosen under theinfluence of moisture, such as dew and rain, and therefore no longerproperly hold packages or containers together.

SUMMARY OF THE INVENTION

Starting out from this prior art, the object of the invention is to makeavailable a joining element of the type mentioned at the outset, whichcontracts over long periods of time, but which on the other hand isrigid under short-term rapidly increasing loads.

According to the invention, this object is achieved by a joining elementaccording to claim 1.

A short-lasting or fairly short-lasting tensile load is considered to beone that builds up and/or reduces over the course of less than 1 minute,in particular one that is shorter than 10 seconds. In applications ofthe invention as repair material for the apparatus of locomotion inhumans, this means for example the load exerted, during walking, on thejoining material that connects the muscles to the bone.

Contraction is also understood as a relaxation of the material, forexample in the sense of a change in shape of the first material or adecomposition. Such a change in shape can also be regarded as adeformation, but one that occurs without application of an externalforce. Moreover, the second material is able to swell and be compressedby the first material transverse to its longitudinal direction, suchthat a contraction takes place. In particular, the swelling of a corematerial in the first material can enforce a change in shape, forexample by changing the angle of intersection in the braid, whichresults in the shortening of the joining element.

The second material is also able to diffuse out of the first material,such that the element shortens, or the second material can comprisethreads that are initially stretched or oriented parallel to thelongitudinal direction of the joining element, and said relaxation takesplace as a result of deformation of said threads in the first material.Threads describe in this context molecules and molecule structures.

In packagings and containers for goods, ropes having the features of theinvention can ensure that the packaging remains securely held by thesurrounding ropes, despite the effects of weather.

The invention permits the use of a method for stimulating healing andfor stimulating biological transformation and regeneration processes ofsoft-tissue parts relative to one another, such as tendons, ligaments,fascias, organ cavities, general connective tissue, vessels, heartvalves, cartilage tissue, etc., or of soft-tissue parts relative tobone, by the gentle, active, partially dynamic compression that can beachieved by using the material described here.

BRIEF DESCRIPTION OF THE DRAWING

The invention is described below in more detail with reference to thedrawings, in which:

FIG. 1 shows a schematic view of part of a joining element shortly aftera test use in vitro or in vivo, that is to say after an implantation,according to a first illustrative embodiment of the invention,

FIG. 2 shows a schematic view of part of a joining element after alonger period of time since the start of said use according to FIG. 1,

FIG. 3 shows a schematic view of part of a joining element shortly aftera test use in vitro or in vivo, that is to say after an implantation,according to a second illustrative embodiment of the invention,

FIG. 4 shows a schematic view of part of a joining element after a longperiod of time since the start of said use according to FIG. 3,

FIG. 5 shows a schematic view of a joining element shortly after a testuse in vitro or in vivo, that is to say after an implantation, accordingto a third illustrative embodiment of the invention,

FIG. 6 shows a schematic view of the joining element after a long periodof time since the start of said use according to FIG. 5,

FIG. 7 shows a schematic view of a joining element shortly after a testuse in vitro or in vivo, that is to say after an implantation, accordingto a fourth illustrative embodiment of the invention,

FIG. 7A shows a cross-sectional view of the joining element illustratedin FIG. 7,

FIG. 8 shows a schematic view of the joining element after a long periodof time since the start of said use according to FIG. 7,

FIG. 9 shows a schematic view of a joining element shortly after a testuse in vitro or in vivo, that is to say after an implantation, accordingto a fifth illustrative embodiment of the invention,

FIG. 10 shows a schematic view of the joining element after a longperiod of time since the start of said use according to FIG. 9,

FIG. 11 shows a schematic diagram for an example of an area of use of ajoining element according to the invention,

FIG. 12 shows a schematic diagram of the thread tension plotted againsttime for a joining element in the form of a thread according to theinvention in a test use in vitro or in vivo compared to a conventionalthread,

FIG. 13 shows a schematic view of a part of a joining element with athread with solid core according to an illustrative embodiment of theinvention,

FIG. 14 shows a schematic view of a part of a joining element with athread with tubular core according to an illustrative embodiment of theinvention,

FIG. 15 shows a schematic view of a cross section through a joiningelement with a multicore thread with an outer membrane according to anillustrative embodiment of the invention,

FIG. 16 shows a schematic view of a cross section through a joiningelement with a multicore thread, with in each case its own membraneaccording to an illustrative embodiment of the invention,

FIG. 17 shows a schematic view of a cross section through a joiningelement with a multicore thread, with an inner common core membrane,according to an illustrative embodiment of the invention,

FIG. 18 shows an experimentally measured curve in which the force takenup by the thread is plotted against time,

FIG. 19 shows two experimentally measured curves in which the shorteningobtained through the contracting thread is plotted against thegranulation for different silicone/salt ratios,

FIG. 20 shows an overview of the experimentally determined ratiosbetween initial shortening (in percent per day), compared to the weightratio of silicone to salt for granulation (in micrometers),

FIG. 21 shows two experimentally determined curves in which theshortening obtained through the contracting thread is plotted in percentagainst time for different silicone/NaCl ratios, and

FIG. 22 shows two experimentally determined curves in which theshortening obtained through the contracting thread is plotted in percentagainst time for different TPE/NaCl ratios.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

FIG. 1 shows a schematic representation of a part 10 of a joiningelement, which comprises a pretensioned core 11 surrounded by a jacket12. The jacket 12 is composed of a rigid material, which is compressedunder the effect of chemical and physical processes that take place overthe course of time and are described below. The resulting force thattriggers this compression process is the force resulting from thepretensioning of the core minus the tensioning force acting on thethread from the environment (for example the tensioning force appliedduring stitching). As the tensioning force exerted on the thread by theenvironment decreases, the resulting compressive force acting on thejacket increases. This favors the compression of the jacket, resultingin an accelerated contraction of the thread or of the textile structureformed from the latter. This results in a tensioning of the thread or ofthe textile structure until an equilibrium is once again establishedbetween the forces described above, or the jacket is able to support thecompressive force acting on it, without slow compression.

The material for the jacket is characterized in that it permitscontrolled plastic deformations over a defined period of time, i.e. thematerial has a distinct yield point and behaves substantiallyelastically below the yield point. This means that the main component ofthe material should have a glass transition temperature above bodytemperature or should have a high crystallinity and additionally has ahigh degree of fracture toughness. Typical representatives of this classof materials are, for example, blends or copolymers of structuralpolymers with a Tg distinctly above body temperature and polymers with aTg distinctly below 0° (blend: polylactides with trimethylenecarbonates, copolymer: polyhydroxybutyrate with polyhydroxyvalerate).However, this function can also be performed by highly crystallinepolymers such as PE, polyamides or polyesters, in which case thestructure of the envelope would have to be provided with defined yieldpoints, for example by local thinning of the cross section,incorporation of reinforcements and kinks, or local periodic variationof the modulus of elasticity by variation of the polymer orientation. Atthe ends of this part 10 of the joining element there is in each case ajoining construction 13, for example a mesh, with which the jacket 12 iswoven. The core 11 is routed through this mesh 13 and, for example,knotted 14. The core 11 itself is composed of a flexible material.Examples of materials for the core are preferably materials of anelastomeric nature and with minimal tendency to creep, typicalrepresentatives of which are crosslinked polymers such as silicones orpolyurethanes, which can also be composed of degradable components ifcomplete degradation of the thread is sought. In the rest position, thecore 11 is shorter than the distance between the joining constructions13, such that the inserted core 11 in the view in FIG. 1 ispretensioned. This is indicated by the arrows 15. Since the jacket 12 isrigid, the joining constructions 13 are kept spaced apart despite theeffect of the spring tension of the core 11.

The functions of the core and jacket as described here can also beinterchanged, i.e. before processing the jacket is pretensioned and thecore is acted on by pressure.

It is also possible for the pretensioning to be applied only after theprocessing (for example after the stitching in the case of the thread).

A joining element, in particular a suture material for wound treatment,for example also a wide band, can be made up of many such parts 10 ofjoining elements, in which for example many joining elements arearranged alongside one another and in succession, in order to form aband that can be processed. The joining elements are advantageouslysurrounded in their entirety by an envelope with controlled kinkingbehavior. However, it may also be possible for each individual elementto be surrounded by such an envelope, particularly if the wholeconstruction is to be as flexible and formable as possible.

If a large force quickly builds up on such a band and abates again aftera certain time, for example a force that builds up in tenths of seconds,possibly lasts for a few seconds and then returns to zero, the rigidjacket 12 then holds the individual parts 10 in position and thus alsothe band and, consequently, the organs connected thereto, for example atendon and a bone.

FIG. 2 now shows the development of a part 10 of a joining element overa long period of time, for example over several weeks. After a longperiod of time, possibly interrupted by forces of the short-lasting typementioned above, the jacket 12 deforms, here designated as changedjacket by reference number 16. By means of the pretensioning effect ofthe core 11, the joining constructions 13 move toward one another, andthe band made up of the parts 10 of the joining elements contracts. Thisresults in a change in length of up to 80 percent from the originallength.

Instead of a deformation of the jacket 16, the jacket 22 according toanother embodiment can also structurally decompose, for example by theat least partial use of the aforementioned biodegradable polymers, thatis to say at least part of the material initially loses some of itsmodulus of elasticity and thus its stability against kinking, as aresult of the uptake of water and the incipient hydrolysis of theincorporated biodegradable polymers, but at the same time gains in termsof its plastic deformation capacity. As the degradation proceeds, thisresults in loss of mass and physical breakdown. This is shown in FIG. 3at the start of use and in FIG. 4 after a long period of time. Similarfeatures are in each case provided with the same reference numbers inall of the drawings.

The part 20 of a joining element is provided with a jacket 22, whichloses its structural integrity over the course of time. This can be seenfrom the thinner jacket 26 in FIG. 4. The degrading jacket 26 thusoffers less resistance to the flexible core 11, and the distance betweenthe joining constructions 13 becomes shorter. If, however, rapid tensileor impact forces act on the joining element 20 during this process, thenit again reacts rigidly, because the stiffness properties of the jacket22 have not in principle been changed by the deformation, particularlyin relation to its resistance against rapid stressing, they are notmacroscopically different (departing from the only schematicrepresentation in the Fig.), and have only become weaker relative to thecore 11. This involves in particular the elastic properties of thejacket material that are of relevance in short-term stressing.

Impact forces can be taken up if planar or three-dimensional bodies areformed from the joining elements, which bodies have a buckling orkinking stability defined by their cross section. This can be achieved,for example, by a sheet of interconnected rotationally symmetricalthreads or by the fact that the interior of the joining element iselongated with an oval or ellipsoid cross section.

In an illustrative embodiment not shown in the drawings, the joiningelement 10 or 20 can also have a rigid core and a pretensioned jacket.The function according to FIGS. 1 to 2 and 3 to 4 remains the same,however. The important point is that each part 10, 20 does not react torapid load changes, in other words remains rigid, while it contractsover the course of time.

It is clear that such one-dimensional elements can also be given atwo-dimensional or three-dimensional arrangement, such that contractingtextile structures are obtained. It is also possible for these materialsto be provided with resorbable constituent materials, such that thesematerials can finally disintegrate.

FIG. 5 shows a third illustrative embodiment of a joining element 30.The joining element 30 is made up of a multiplicity of adjacentmolecules 31 (core polymer) that have an incorporated lubricant 32. Themolecules can, for example, be polymeric macromolecules of knownbiocompatible polymers. The so-called lubricant, which acts for exampleas a plasticizer, can involve in particular, but not exclusively, asolvent for the core polymer or also substances with a high degree ofsolubility in the core polymer, this substance having to bebiocompatible in the released doses. It can involve low-molecular-weightsolvents such as acetone or alcohols, or also N-pyrrolidone ordimethylsulfonamide (DMSO), which are known to be tolerated inrelatively high doses. Gradually, for example over periods of weeks, thelubricant 32 leaves the thread, as is indicated by reference number 33for the arrows; in other words the lubricant is diffused out. Thekinetics of the diffusion are on the one hand determined by themolecular interactions between the core polymer and the lubricant, andon the other hand the diffusion behavior can be controlled by theapplication of organic (for example another polymer of low solubilityfor the lubricant) or inorganic (for example CVD layers such asplasma-polymerized PMMA or SiOx or amorphous diamond-like layers),biocompatible barrier layers. In this way a force acts in particularalong the arrows 34. The joining element 30 thus converts to acontracted state according to FIG. 6, in which each molecule 31 takes upless space. These joining elements 30 can be similar to threads, but canalso be composed of several textile filaments.

FIG. 7 shows a fourth illustrative embodiment of a joining element 40.The joining element 40 comprises a core 41 surrounded by a jacket 42.The core 41 is a swellable material, for example as mentioned below. Thejacket 42 is composed in particular of a mesh, for example of threads 43arranged helically around the core 41, in particular braided orinterlacing threads 43, in particular from the group of known degradableand nondegradable polymers which have been described and processed forsuture materials and which typically are used in surgical suturematerials, for example stretched polyesters, polyamides, polyolefins,polyaramides, expanded or densely halogenated polymers or high-strengthladder polymers such as polyetherether ketone, captones. FIG. 7 showsthe joining element 40 in the rest state, where the threads 43 areoriented for example at an angle 44 of 30 degrees with respect to thelongitudinal direction of the joining element 40. The angle can in itsinitial state be between 5 and 50 degrees for example, in particularfrom 10 to 40 degrees, and is preferably 20 to 35 degrees. Thus, theillustrative embodiment depicted here falls midway in this interval.

Such a joining element 40 does not react to rapid changes in force. Bycontrast, a swelling of the core 42 caused by chemical and physicalprocesses leads to a thickening of the core 42 surrounded by the thread43. In this way, the angle 44 with respect to the longitudinal directionof the joining element 40 changes to a new angle 45, for example of 48degrees. The mesh 46 is thus imparted a greater diameter and shortens,as does the entire joining element. When made up of braided threads, themesh is designated as a braid. This term can accordingly replace theword mesh throughout the application.

The swelling process can be achieved for example by an osmotic core 42,that is to say a core 42 which with an osmotically active substance (forexample salt, particulate form of a water-soluble substance (for examplesaccharides) or highly concentrated solution of these substances in anelastic tube), which accordingly takes up water.

For example, as is represented very schematically in FIG. 7A, the core42 can comprise a filamentary polymer material (not degradable, or alsocompletely or partially degradable), for example a thermoplasticelastomer (polyurethane, polyester), a crosslinked elastomer (silicone,polyurethane, elastin, collagen) or a gel (polyethylene glycol,alginate, chitosan) in which salt crystals 47 are incorporated, whereinthe particulate substance can advantageously have a concentration ofbetween 5 percent and 75 percent by volume in the polymer depending onthe particle size, particle size distribution and state ofagglomeration. When nanoscopic particles are used, however, the highparticle count means that concentrations of less than 1% are alreadyeffective. The polymer thread can be extruded from the melt or from thesolution, and the particles are co-extruded or admixed to the polymermass before extrusion. They can also have a concentration of 25 to 60percent. Since individual alveoli form around the particles as thesurrounding liquid is taken up, the strength of the core (the threadstrength is determined by the properties of the surrounding filaments)is directly dependent on the concentration of the particles.

In another illustrative embodiment, a tube can be provided with amembrane, for example a PU membrane, of 10 to 200 micrometers into whichthe expanding material or the osmotically active substance or its highlyconcentrated solution is directly filled. Therefore, except for thepacking density, 100 percent of the volume is filled with theosmotically active substance or the salt. The tube can be made of PUR,siloxane, PEG or other permeable, in particular semipermeable productsin the from of osmotic, elastic or plastic and geometrically extendiblemembranes (e.g. stretching of axial folds, pleats or undulations). Inparticular, the tube can be narrowed at regular intervals in order toform segmented chambers. This means that the overall thread can be cutto any desired length, without substantially influencing the describedeffect.

The osmotically active substances can include biocompatible inorganicsalts and aqueous solutions thereof, for example sodium chloride (NaCl)or calcium chloride, calcium carbonate, tricalcium phosphate, ororganic, osmotically active molecules can be used, for examplelow-molecular-weight polysaccharides such as dextran. To improvehandling and to further influence the kinetics of osmosis, theosmotically active substances can also be embedded in a biocompatiblegel or hydrogel (for example from the group of alginates, chitosans orcopolymers thereof, polyacrylates, polyethylene glycol, etc.) or, asexplained above, in an elastomer. An effect whose action is comparablein principle to the osmotically active substances can also be achievedby sole use of hydrogels. According to Fick's laws, particularimportance is attached to the membrane surrounding the swelling system,which membrane critically influences the kinetics of osmosis by virtueof its permeation and diffusion properties for H₂O, and also by virtueof its thickness. The membrane can of course be made up of severallayers or can also be provided with stable or solublediffusion-inhibiting layers. If hydrogels are used, such a membrane-likeproperty can also be achieved by means of a crosslinking density thatincreases considerably toward the outside. The concentration differenceseffecting osmosis are to be achieved between thread core and surroundingblood or interstitial and/or intrastitial fluid of the patient.

The braided arrangement of the threads 43 can be obtained using textilethreads, as are typically used for degradable or nondegradablemonofilament or multifilament suture materials, for example stretched ortextured polyesters, polyamides, polyolefins, polydioxanones. The suturematerial can be constructed from a swell core surrounded by the braidedthreads and also from several interwoven swellable threads each in turnsurrounded by a threaded braid. The filament diameters are in line withthe prior art in terms of the fineness of the core that is to besurrounded and in terms of the choice of a monofilament or multifilamentcovering yarn (0.2-200 micrometers). This shortening mechanism, actinglike a sliding lattice, can also be achieved analogously with a threadequipped with a swell core, with a swelling coating of the structuralfilaments, in particular of the structural filaments forming the braidor additionally axially extending structural filaments. As has alreadybeen stated concerning the other illustrative embodiments, contractingtwo-dimensional or three-dimensional textile structures can also becreated using said thread materials.

In other words, the joining element 40 is given long-term degrees offreedom, with the result that the material slowly relaxes or contractswithout application of force. At a peak load, by contrast, the joiningelement 40 reacts rigidly. Of course, in accordance with the prior art,all materials or material surfaces coming into contact with thebiological tissue can be chemically, biochemically or biologicallyfunctionalized, for example by adsorption, grafting or release ofbiologically active substances such as growth factors, inflammationinhibitors, cytokines, receptors or receptor sequences, antibiotics, orsubstances that have an antibiotic, cytostatic, bactericidal orbacteriostatic effect.

FIG. 7A shows a further functionalization, according to the invention,of the joining element. The swelling core 41 comprises vesicles 48charged with active substance, or comprises interstitially dissolvedactive substances 49, which are thus incorporated between polymerchains. By means of the swelling, the pressure on the vesicles and onthe dissolved active substances increases. Therefore, active substancecan be actively driven out of the core. By varying the radialdistribution density of the vesicles, it is possible to obtain atime-controlled release profile, which is of course also influenced bythe swelling pressure that builds up. If the core is provided with, asdescribed above, a diffusion-controlling membrane, the flow of substanceout of the core can additionally be influenced by the transportproperties of the membrane that are dependent on concentration and onchemical activity. The reference numbers 47, 48 and 49 have, for sake ofclarity, been indicated at different locations of the core 42. Inprinciple, the salt particles 47 can be distributed isotropically in thecore. The active substances can advantageously be provided either invesicles 48 or be interstitially dissolved, but in both configurations,and in contrast to the simplified representation, there is an isotropicdistribution across the core.

In other words, a swelling effect will be achieved by hydration of amacromolecule structure. A tubular elastic membrane is fitted in a meshsleeve made up of rigid threads that wind in a helical formation aroundthe tube. Tensile forces are transmitted via this mesh sleeve. In theinterior of the tube there is a saturated salt solution. Mesh sleeve andmembranes are placed in an isotonic solution. By means of achemical/physical process, a concentration balance takes place until astate of equilibrium is obtained. As a result of the solvent being takenup, a considerable pressure builds up in the interior of the elastictubular sleeve and results in a swelling of the tube. A forceequilibrium is established between the internal pressure and a tensileforce that is applied to the mesh sleeve or braided sleeve in the axialdirection. The mesh sleeve acting as a sliding lattice contracts.

A simulation has been conducted in order to calculate the longitudinalcontraction force and the changes in dimension caused by the osmoticpressure at a given concentration difference (Δc) [mol/l] on both sidesof the membrane for 310 degrees Kelvin:

Thread diameter at start d₀ 7 × 10⁻⁴ m Starting angle α  60° Threadangle to tension direction β 90-α° Concentration body C_(blood) 0.296mol/l Saturation concentration (NaCl) C_(saturation)  6.15 mol/l

The osmotic pressure Π [Pa] for ideally diluted solutions can be set outin a simplified manner as follows:

Π−Δc·R·T=(c _(saturation) −c _(blood))·R·T

Radial tension σ_(radial) [N/m] with boiler formula:

$\sigma_{radial}\frac{\pi \cdot d_{thread}}{2}$

Radial force (f_(radial)) [N/m] from tension (σ_(radial)):

$\left( \sigma_{Radial} \right) = {\frac{F_{radial}}{_{{circum}.}} = {\frac{\Pi \cdot d_{thread}}{2} = f_{radial}}}$

Thread diameter (d_(thread));

$\left( d_{thread} \right) = {d_{0} \cdot \frac{\cos \mspace{11mu} \alpha}{\cos \mspace{11mu} \alpha_{0}}}$

Ratio of radial force (F_(radial)) to longitudinal force (F_(long)):

$\begin{matrix}{{F_{{long}.} = F_{radial}}{{\cdot \tan}\mspace{11mu} \alpha}} \\{= {{f_{radial} \cdot \tan}\mspace{11mu} {\alpha \cdot _{{circum}.}}}} \\{= {{\frac{\Pi \cdot d_{thread}}{2} \cdot \tan}\mspace{11mu} {\alpha \cdot d_{thread} \cdot \Pi}}}\end{matrix}$ $\begin{matrix}{F_{{long}.} = {{\frac{\Pi \cdot d_{thread}^{2}}{2} \cdot \tan}\mspace{11mu} {\alpha \cdot \pi}}} \\{= {\frac{\left( {c_{saturation} - c_{blood}} \right) \cdot R \cdot T}{2}{\left( {d_{0} \cdot \frac{\cos \mspace{11mu} \alpha}{\cos \mspace{11mu} \alpha_{0}}} \right)^{2} \cdot \tan}\mspace{11mu} {\alpha \cdot \pi}}}\end{matrix}$

Pressure force (F_(pressure)) [N]:

$F_{pressure} = {{\Pi \cdot A} = {\Pi \cdot \frac{d_{thread}^{2}}{4}}}$

Relative length (I) [%]:

$= \frac{\sin \mspace{11mu} \alpha}{\sin \mspace{11mu} \alpha_{0}}$

Relative volume (V) [%]:

V=l·d _(relative) ²

Resulting length-contraction force (F_(res)) [N]:

F _(res.) =F _(long.) −F _(pressure)

At a difference of Δc=5.8 mol/l, it has been found that the resultinglength-contraction force is maximum at a defined thread angle ofapproximately 30° and at the starting dimensions. As the volumeincreases, the surface area and thus the pressure force (F_(pressure))becomes greater, such that the resulting length-contraction forcedecreases. The proportion of the radial force becomes greater than thelongitudinal component starting from an angle of 45°. The desiredminimum of the longitudinal force is achieved in this example at athread angle of 48°. At this point, the thread has shortened by slightlymore than 20%. A corresponding representation is shown in FIG. 11.

FIG. 9 shows a schematic view of a joining element 50 shortly after atest use in vitro or in vivo, that is to say after an implantation,according to a fifth illustrative embodiment of the invention. Thejoining element 50 is a thread made up of a base material 51, forexample composed of the customary degradable or nondegradable suturematerials, in which thread molecules 52 are incorporated. The molecules52 can for example be polymers with a glass-transition temperature wellbelow body temperature, or polymers can be chosen which have a markedtendency to take up water and swell (for example polysaccharides,polyamides) or also polymers, or polymers whose previous crosslinking isreduced by the hydrolytic degradation of the crosslinking sites, suchthat the contractility of the molecules is increased, and which, forexample by means of processing and their limited solubility in the basematerial, can form molecular strands or also mesoscopic structures, forexample nematic structures.

The threads are stretched during production, such that the contractilethread molecules or phases 52 are oriented parallel to the longitudinaldirection of the joining element 50. When a force is applied rapidly,that is to say a traction or impact, the joining element 50 reactsrigidly via the threads 52. Over a long period of time, for exampleseveral days and in particular several weeks, the thread molecules orphases 52 deform, in particular they contract and coil up or expandtransverse to the original direction of stretching. In doing so, theyleave the longitudinal orientation and thus become shorter relative tothis longitudinal orientation. A comparable thread section thus becomesshorter. If, during this process, rapid traction or impact forces act onthe joining element 50, it again acts rigidly, since the stiffnessproperties of the threads 53 have not basically been changed by thedeformation. Although the modulus of elasticity of a coil structure issignificantly less than that of an oriented, nematic structure, thisstructure, from the mechanical point of view, takes up only a small partof the short-lasting loads on the joining element 50. The stiffness istherefore not appreciably affected by such an impact-type load.

FIG. 11 finally shows, in a schematic representation, a diagram of anillustrative embodiment according to the invention, in particular anexample of a range of use of a joining element according to theinvention. The thread angle with respect to the tension direction isplotted in degrees on the X-axis, which angle has been provided with theletter β in the above formulae. On the Y-axis, the force F_(res) innewtons is plotted on the left-hand side, while the right-hand sideshows the relative diameters (reference number 61), lengths (referencenumber 62) and volumes (reference number 63) in percent. The threadangle range defined by the box 64 covers a change in volume of over 50percent. The corresponding force curve 65 shows a not all tooasymmetrical force distribution, and thus not too great a drop, aroundthe maximum load of the thread element.

A method for treating tissue and prosthetic material comprises themethod step of connecting tissue and/or prosthetic material with ajoining element according to the invention. Prosthetic material caninclude thread or mesh material without needle, which is secured as aprefabricated thread loop on one or more suture anchors or similarimplants. The prosthetic material can also include thread material witha needle, which is secured as a prefabricated needle with thread loop onone or more suture anchors or similar implants. In particular, a bandproduced from the thread material can also be connected directly to thebone or soft tissue, for example, by means of a staple or pin or nail.

The joining element, which shortens over the course of time, is used inthe fixation of tendons or ligaments to bone. A further use of thejoining element, which shortens over the course of time, in combinationwith suture anchors, secured fixedly or sliding, is as a loop or aconnection between anchor retention plates (parachutes) or a connectionbetween several anchors. The joining element, which shortens over thecourse of time, can also be used in mammals and other animals, inparticular in humans.

In particular, the joining element, which shortens over the course oftime, can be provided for surgical use in connection with the followingapplications: tendon reconstruction, in particular Achilles tendonreconstruction or rotator cuff reconstruction, shoulder stabilizationoperations on the glenoid, tendon transfers, for connecting tendons,fascias, ligaments or other soft-tissue parts, joint stabilizationoperations, for example on the joint capsule, joint stabilizationoperations, in particular acromioclavicular or sternoclavicular jointstabilization, collateral ligament reconstructions, for example on theknee, elbow or ankle, cruciate ligament reconstruction, closure offascial gaps, hernia operations, wound closure in open-wound treatment,for example after fasciotomy, skin sutures, reconstruction of tendons,bones or soft-tissue parts on implants of all types, resorbable ornonresorbable, for example on prostheses or suture anchors, ligatures,fixation/suspension of uterus or bladder, suturing of intestine,stomach, bladder, vessels, trachea, bronchi or esophagus, and suturingof fascias.

The joining element, which shortens over the course of time, can be usedas tissue. It can also be used as a pouch for enclosure of organs, forexample the heart. The tissue can also be used for fascial gaps.

The tissue can be used as bridging graft for tendons or fascia defects.It can also be used for closure of skin defects, for example incombination with artificial or cultivated skin or other skin-closurematerials, or serves as a cuff around vessels, for example in ananeurysm, around bile ducts or the gallbladder, around parts of theintestine, for example the stomach. Finally, the tissue can also beprovided for external application, for example as support stockings,burns coverings for scar correction or the like. Moreover, the tissuecan also serve as a bridging graft for several tendons at the same time,if these are connected to different sections, for example on the rotatorcuff

It may be particularly advantageous for the material to be provided inprefabricated form, that is to say in the form of the organs or organparts that are to be replaced or augmented, for example as cruciateligaments, tendons, retinacula, fascias, etc. Moreover, the threadmaterial can be provided with functional surface structures, for examplewith barbs for fixation of soft-tissue parts. Finally, there is theconnection of the thread material to bone suture anchors, sliding in theanchor or not sliding, for knotting or in a knotless configuration. Itcan be produced from non-resorbable, partially resorbable or completelyresorbable materials. In order to distinguish between differentproperties, joining elements can be produced and used in differentcolors.

In addition to being used alone, they can also be provided incombination with rigid one-part or multi-part implants, for example withan inherently displaceable compression plate that contracts in a desiredmanner during contraction of the thread.

In addition to these uses, the joining element can also be used for theconnection of technical objects, for example for the connection oftextile sections or fastening elements generally. The description of theuse of illustrative embodiments in medicine does not imply anylimitation to this use.

FIG. 12 shows a schematic diagram of the thread tension 72 plottedagainst time 71, for a joining element in the form of a thread 84according to the invention in a test use in vitro or in vivo, comparedto a conventional thread 74.

The broken line 73 indicates an arbitrary threshold above which a threadwould be designated as taut (high thread tension) and below which athread would be designated as rather loose (low thread tension).

The curve 74 relates to a conventional thread, the curve 84 to a threadaccording to the invention. Close to the starting time of animplantation for securing a ligament for example, the tensions of boththreads are comparable. The conventional thread gradually loses tension,as is represented by the monotonic downward line 75. In the event of afall 76, which can also be any inappropriate movement on the part of theperson with the sutured ligament, there is a sudden increase in tension,whereupon the subsequent monotonic downward line 77 drops further to astill lower level.

By contrast, in the case of a thread 84 according to the invention,there is a monotonic increase 85 in the thread tension over the courseof time. This is important, because a fall 86 of the same amplitude,here occurring at the same time as the fall 76, also leads to aloosening of the thread after the short-lasting increase in tension isremoved. However, the drop is not so great that the tension after theevent lies substantially below the starting tension. There is then arenewed tightening 87 of the thread, after which a higher tension valuecan again be achieved. This cycle can repeat itself several times inorder to compensate for dislocations of the healing tissue parts untilcompletion of the healing process, which is completed after severalweeks, by contractile reunion of the tissue parts.

FIG. 13 shows a schematic view of a part of a joining element 160 with athread with solid core according to an illustrative embodiment of theinvention. This represents a special configuration. The thread 160 iscomposed of a core 161 and of a mesh sleeve 162. The mesh sleeve 162 isin this case made up of twelve braided filaments 163. The filaments aremultifilaments that take up an oval space. In this way, it is possiblefor the braiding to completely cover the core 161. Instead of twelvefilaments 163, it is also possible to provide more (for example 14, 18or more) or fewer (for example 3, 4, 6 or 10) of said filaments 163.With a higher number, it is also possible for the filaments to bemonofilaments. The core 161 here is delimited by an elastically,plastically or geometrically radially extensible membrane and containsno, one or several (here three) stitch threads 164 for taking up strongtensile loads, for example in the event of falls 86. In the core 161,there is also a gel or a matrix 165, in which it is possible toincorporate osmotically active, particulate substances 166, orsubstances enclosed in vesicles, for example salt crystals. The saltcrystals can also be replaced by other osmotically active substances.These inclusions 166 can then take up liquid by osmosis, in the mannerdescribed above, and, by expansion of the core, can lead to a shorteningand therefore tightening of the thread 160. This shortening is supportedby the crosswise arrangement of the sleeve filaments 163, whereas thecentral stitch threads define the maximum strength of the thread 160 andat the same time limit the compression of the core 161.

FIG. 14 shows a schematic view of a part of a joining element 170 with athread with tubular core 161 according to an illustrative embodiment ofthe invention. The thread 170 is composed of a core 161 and of a meshsleeve 162. The same reference numbers have the same meaning or similarmeaning in all of the illustrative embodiments. The core 161 comprises atubular membrane 177, which can be provided with a coating 171. As hasbeen described in the earlier embodiments, the coating can influence thediffusion properties or also reduce the friction between the core andthe shearing filaments, for example, and thus increase the efficiency ofthe osmotic process, or it can be designed as an axially folded, pleatedrigid membrane (in contrast to the smooth elastomeric membrane 177) andlimit the swelling process and obstruct swelling of the core out of thebraid. Examples of materials for substance transport: PVD coating or CVDcoating or polymer coating; for limiting the expansion: stiff structuralpolymer such as polyamide or polyolefin.

The three stitch threads 164 are surrounded by a saturated salt solution175 or by another osmotically active substance, in which furtherparticulate salt crystals 176 can be present for taking up furtherliquid for maintaining the saturated solution. The mesh sleeve 162 withthe filaments 163 is designed in the same way as in the previousillustrative embodiment. The liquid can be, for example, an aqueoussolution, a hydrophilic liquid (for example higher alcohols, DMSO), or ahygroscopic, biocompatible liquid or a hydrophobic liquid (examplesoils). The degree of hydrophobicity of the liquid can be used toinfluence the speed of diffusion and therefore the kinetics of theosmotic effect. Analogously to the embodiments described in FIG. 7, thestitch threads can also be embedded in a gel-like or elastomeric matrix,in which osmotically active substances in solid or liquid form areincorporated in order to achieve the osmotic swelling. If the matrix issufficiently stable in itself, for example in the case of an elastomericmatrix, it is also possible to dispense with the membrane 171.

The coating could also be of TPU. Stitch threads, in analogy with whathas been described above, can also be omitted, can be present in adifferent number, or can be applied on the outside of the core.

As a variation to the embodiment shown in FIG. 14, FIGS. 15-17illustrate different designs of the thread structuring. FIG. 15 shows aschematic cross-sectional view of a joining element 180 with a multicorethread 161 with an outer membrane 181 according to an illustrativeembodiment of the invention. Three cores 161 are provided here, whichare surrounded by an osmosis membrane and which, for example, each havea gel filling 165 in which salt crystals 186 are embedded. Depending onthe strength of the thread that is to be produced, it is also possibleto provide four, five, six or more cores 161 which are surrounded forexample, but not necessarily, by a membrane on which the filaments 163of the sleeve 162 are arranged. The (multi)filaments 163 of the sleeve162 each comprise a multiplicity of individual filaments 183 which arepresent in the depicted form as a result of the tensile stress that isexerted. The thread 180 as a whole is surrounded by a sleeve 181, whichseals the thread off from the outside. In contrast to the threads inFIGS. 13 and 14, the braided filaments 163 here are inside the osmoticchamber. In particular, the space 185 can also be filled by the solutionwhose concentration decreases as a result of the uptake of liquid. Thespace 185, and also the spaces enclosed by the membranes 163 and 181,can contain vesicles 187 filled with active substances, or can directlycontain active substance solutions 188, which are subjected to pressureby the radial expansion of the core structures and thus expel one ormore active substances, which are released through the membrane 181 intothe surrounding tissue. As in the other illustrative embodiments,specific features of this illustrative embodiment too can be replaced byother features described here, for example as regards the number andposition of stitch threads.

FIG. 16 shows a cross section through a joining element 190 with amulticore thread 190 with in each case a core membrane 191 according toan illustrative embodiment of the invention. The three cores 164 hereare each surrounded by the osmotic liquid or gel or elastomeric polymer165 with incorporated salt crystals 186, which as a whole, and per core164, is closed of by an osmotically acting membrane 191 (or in the caseof the elastomer also only a core without membrane, otherwise possiblyalso a core without stitch thread if this structure is inherently stablewith or without membrane). The braided mesh sleeve 162 is providedaround these closed cores 164, which can be twisted or areadvantageously arranged in parallel alongside one another. The space 195between the core membranes 191 and the inner filaments of the meshsleeve 162 can be filled initially upon expansion of the membrane 191,before the desired shortening of the thread. An onset time is thusprovided in the thread which, referring back to FIG. 12, can lead at thestart to a monotonic increase in tension.

FIG. 17 shows a schematic cross-sectional view of a joining element 200with a multicore thread 164 with an inner common core membrane 201according to an illustrative embodiment of the invention. This is anembodiment which, in terms of its features, lies between the embodimentsin FIG. 15 and FIG. 16. The core membrane 201 here is arranged insidethe braided mesh sleeve 162, but instead of surrounding each individualcore 164 it surrounds the cores 164 as a whole, such that the space 185lies within the membrane 201 and can also be used, as is illustrated inFIG. 15, for the inclusion of systems that release active substance. Themesh sleeve 162 then surrounds these.

From these illustrative embodiments, it will be clear that the inventionis not intended to be limited to one of these illustrative embodiments.Instead, every combination of these features is also covered by theinvention. Thus, the individual threads with the stitch threads 164 canbe a liquid, gel-like or polymer substance. However, it could also haveno stitch thread as such, but only the matrix; several matrix threads inthe core could be of advantage in the case of threads of relativelylarge calibre, because they make the thread softer, and, in addition,the diffusion kinetics with several small-calibre threads areaccelerated compared to those with a large-calibre thread.

The number of stitch threads (here three) can be varied between none andseveral dozen. The mesh sleeve 162 is here composed of a multifilament163 with in each case nineteen monofilaments 183. It is clear that boththe nature of the multifilaments 163 and also the number of themonofilaments 183 can be varied. The former number can be chosen inparticular between three and ten, and the latter number between ten andover one hundred. In the case of a relatively rigid inner membrane, itis possible in some cases to do without a complete covering of the meshsleeve, since the membrane cannot then protrude between the defects inthe cover. It is important to have a membrane sleeve which permits thediffusion but at the same time limits the pressure difference, such thatfailure of the membrane can be reliably avoided. This purpose is alsoserved by the stitch threads 164, which take up sudden tensile loads andreliably avoid excessive compression of the core of the thread in theevent of falls. It is thus clear to a person skilled in the art thatfeatures of all the illustrative embodiments described can be combineddirectly with one another and interchanged.

A number of tests have been carried out using suitably prepared threadsand are set out as examples of possible illustrative embodiments. Thus,the curve in FIG. 12 has been verified by a test involving lifting of aweight. This is shown in FIG. 18 by a curve 303 in which the liftedforce 302 is plotted against time 301. The tested thread is a threadaccording to FIG. 13 (but without stitch threads 164 and membrane 161)with a weight ratio of silicone matrix to salt of 1:1, where theparticle size of the crystals 166 is smaller than 70 micrometers andwhere the thread is securely fixed in distilled water at a temperatureof 37 degrees Celsius. The thread tension is measured continuously. Thetensile force (thread tension) increases in less than one day to over 12newtons, in order then to move to a state of equilibrium limited by thesleeve. The thread has become deliberately loose after two days, whichcorresponds for example to a fall by the patient with a ligament suturedby such a thread. The loosening can be achieved simply by a lengthening.The thread tension build-up thus begins anew, but this time to a lesserextent, the built-up spring tension only reaching a tensile force of ca.8 newtons. The state of equilibrium was maintained here for just underthree days in order to carry out a renewed loosening. In this thirdarea, after 5 days and more, tension can be built up over 4 newtons, theflat curve 303 now showing that the maximal tension in the thread hasbeen built up.

FIG. 19 shows a schematic view of two curves 403 and 404, in which thetime until the maximum shortening 402 has occurred through theshortening thread is plotted against the granulation 401 for differentsilicone/salt ratios. FIG. 18 had a silicone/salt ratio of 1:1. Thismeans that the filling 165 has been to crystals 166 in a ratio by weightof 1:1. The two curves 403 and 404 show the duration up to the maximumshortening as function of the granulation 401 of the salt crystals, thisduration being shorter at a ratio of 2:1 silicone to salt than at aratio of 0.71:1, that is to say if more salt is contained in the core.It should be noted that these are not general rules but experimentalresults, the characteristics of which can change significantly as afunction of further parameters, for example the local distribution ofthe salt crystals, the agglomerate formation and the structure of thepolymer. In the small granulation range of below 50 to ca. 150micrometers, hardly any differences arise, whereas at greatergranulation the duration until the maximum shortening increases rapidly.

The three-dimensional curve 504 in FIG. 20 provides an overview of theratios between initial shortening 501 (in percent per day) relative tothe ratio by weight of silicone to salt 502 for the granulation 503 (inmicrometers). A lot of silicone relative to the salt and smallgranulations provide a rapid shortening in time, whereas both largegranulations and also a higher salt content lead to a smaller shorteningper day. By suitable choice of the individual components, a personskilled in the art can therefore define the behavior of the thread to alarge extent.

The following should be noted in particular. Joining elements in theform of a thread can be produced in diameters of as little as 50micrometers (and less), if it is surgical applications that areconcerned. For thicker threads, a twisted or drilled structure can beformed, generally expressed as a multifilament structure. The advantageof these is that, in the joining elements thus produced, the rubbing ofthe individual threads affords greater strength, while on the otherhand, for the same reason, the large number of twisted or drilledthreads provides a reduced stiffness.

In a thread of 50 micrometers diameter, it is expedient to use powdersof the salt crystals of less than 100 nanometers to 1 micrometer.

From each of these crystals, small centers of osmotic activity areformed. In particular, these centers, which involve vesicles formedaround such salt cores, should be smaller by a factor of approximately10 than the diameter of the swelling core. A small number of centersprovides a more reliable osmotic activity than with a few largecrystals. The speed of the shortening of such threads, corresponding tothe teaching of their construction, is advantageously set by theproperties of the polymer material used for the swelling core.

FIGS. 21 and 22 each show a view of two measured curves, in which theshortening 602 afforded by the contracting thread is plotted in percentagainst time 601 for different silicone/NaCl (salt) ratios 603/604 andfor different TPE/NaCl (salt) ratios 605/606.

It will be noted that, in a silicone thread with a mass ratio ofsilicone to NaCl of 2:1 at an average particle size of the salt crystalsof less than 70 micrometers and a constant thread tension of 1 newton, astate of equilibrium of the curve 603 is obtained after about one day athigh shortening level. By contrast, a four-times smaller shortening isseen at a mass ratio of silicone to NaCl of 5:7 at an average particlesize of the salt crystals of less than 200 to 250 micrometers and asubstantially constant thread tension of 1 newton in the curve 604,which is achieved after about 4 days. The core had a diameter of 0.7millimeter.

The tests with TPE threads were carried out in another time horizon. Itwill be noted that, in a TPE thread with a mass ratio of TPE to NaCl of1:1 at an average particle size of the salt crystals of less than 160 to200 micrometers and a constant thread tension of 1 newton (that is tosay as in the other test), a state of equilibrium of the curve 605 afterca. twenty to twenty-five days is obtained at a very small shorteninglevel of one percent. By contrast, an eight-times greater shortening canbe seen at a mass ratio of TPE to NaCl of 2:1 at an average particlesize of the salt crystals of less than 70 to 150 micrometers and asimilarly constant thread tension of 1 newton in the curve 604, whicheven after more than twenty days has not yet reached a state ofequilibrium.

It is thus evident to a person skilled in the art that, when using TPEand silicone thread cores with different salt content and granulation, asuitable shortening can be set between 40 percent in one day and onepercent in five days, which corresponds to a difference in the speed bya factor 200. These values can additionally be modulated by suitable useof membranes (more or less permeable; more or less flexible inextension). The results presented here with threads having a core canaccordingly be transposed to the other illustrative embodiments.

In addition to silicone, which can be used in different qualities, thisapplies to an even greater extent for threads with TPE filling, that isto say for thermoplastic threads. These thermoplastic elastomers can bevery easily shaped, because they pass through the plastic state duringprocessing. They can be produced in particular in hardnesses of 5 ShoreA to 90 Shore D. Their flowability and their density and otherproperties can be adjusted by compounding with a wide variety of fillersand additives. TPE-V has good rubber-like properties, for exampleethylene/propylene terpolymer/propylene, crosslinked or naturalrubber/polypropylene.

The second material thus comprises a swelling material, in particular ahygroscopic material, such as NaCl, which has the advantage of easilyestablishing a state of equilibrium in the body, without placing toogreat a strain on the patient's body as a result of the osmoticactivity. The swelling of the second material is achieved by osmosis,that is to say by diffusion of water from the space containing liquidsurrounding the joining element (in vitro, for example, water orphysiological saline solution in a beaker; and in vivo by the bodyfluids surrounding the implant site of a thread) through a semipermeableor selectively permeable membrane, which the person skilled in the artchooses as appropriate.

The illustrative embodiments in FIGS. 12 to 22 are in direct relation tothe disclosure of FIGS. 1 to 11. The first material can thus be regardedas the stitch thread or stitch threads and/or axial threads in the meshsleeve and the membrane or axial thread reinforcements in the membraneor membranes. The second material, which slowly contracts over a longerperiod of time, is the one or more chambers 165, 185 in which thecrystals contributing to the swelling are incorporated. A shearing ofthe first material surrounding the second material is afforded inparticular by provision of braided mesh sleeve. The slow contraction ofthe second material over a second period of time longer than the firstperiod of time is understood also as the combination of the effect withthe first material, as arises with the braided thread. The importantfactor is simply that, for in each case two corresponding localreference points in the element, the distance shortens over a period oftime, in other words a tension builds up between these two points. Ifthese points are not firmly fixed, the distance between them shortens,which corresponds to a contraction of the second material.

It is also possible, however, for the membrane itself to be weldedtogether at short axial distances of 3 to 10 times the length of thenormal diameter of a thread at suture points, in order to produceindividual axially defined chambers, which shorten in length uponswelling. To this extent, all uses for the disclosed prosthetic materialare also covered for joining elements designed according to the teachingof FIGS. 12 to 22.

During the shorter-lasting load, a cramping or a spasm can also build upthe tissue dislocation, a peak load and a slightly slower build-up.

LIST OF REFERENCE NUMBERS

-   -   10 part of a joining element    -   11 core    -   12 jacket (originally)    -   13 joining construction (mesh)    -   14 knot    -   15 arrow    -   16 jacket (deformed)    -   20 part of a joining element    -   22 jacket (originally)    -   26 jacket (deformed, in degradation)    -   30 joining element    -   31 molecule    -   33 direction of release    -   34 arrow    -   40 joining element    -   11 core    -   42 jacket (originally)    -   43 mesh    -   44 angle (to begin with)    -   45 angle (later)    -   46 mesh    -   47 salt crystals    -   48 vesicles charged with active substance    -   49 active substances    -   50 joining element    -   51 base material    -   52 thread molecules (to begin with)    -   53 thread molecules (later)    -   61 resulting change in diameter    -   62 resulting change in length    -   63 resulting change in volume    -   64 thread angle range    -   65 resulting change in force    -   71 time    -   72 thread tension    -   73 change-over taut        loose    -   74 conventional thread    -   75 relaxation    -   76 fall    -   77 further relaxation    -   84 thread according to the invention    -   85 tightening    -   86 fall    -   87 further tightening    -   160 thread    -   161 core    -   162 mesh envelope    -   163 envelope filaments    -   164 stitch threads    -   165 matrix    -   166 salt crystal    -   170 thread    -   171 coating    -   175 salt solution    -   176 salt crystals    -   177 tube membrane    -   180 thread    -   181 outer membrane    -   183 monofilament    -   185 space with osmotic liquid    -   186 salt crystals    -   187 vesicles with active substance    -   188 active substance solutions    -   190 thread    -   191 core membrane    -   195 space between cores and envelope    -   200 thread    -   201 multicore membrane    -   301 time    -   302 force lifted    -   303 curve    -   401 granulation    -   402 shortening    -   403 curve for high salt content in silicone    -   404 curve for low salt content in silicone    -   501 initial shortening 501 (in percent per day)    -   502 ratio by weight of silicone to salt    -   503 granulation (in micrometers)    -   504 three-dimensional curve    -   601 time (in days)    -   602 shortening (in percent)    -   603-606 curves for different threads

1. (canceled)
 2. A joining element comprising: a core having a lengththat extends along a longitudinal direction, the core comprising apolymer material and an osmotically active substance distributed withinthe polymer material, wherein the core has a volume capable of swellingalong a transverse direction that is perpindicular to the longitudinaldirection upon exposure to a fluid; and, a diffusion-controllingextendable membrane that surrounds at least a portion of the length ofthe core, wherein the membrane is configured to regulate hydration ofthe core by the fluid, and is further configured to expand along thetransverse direction in response to swelling of the core.
 3. The joiningelement of claim 2, wherein the core comprises an elastomer.
 4. Thejoining element of claim 2, wherein the osmotically active substance hasan isotropic distribution within the polymer material.
 5. The joiningelement of claim 2, wherein the osmotically active substance has avariable distribution density within the polymer material.
 6. Thejoining element of claim 5, wherein the variable distribution densityvaries radially with respect to the longitudinal direction.
 7. Thejoining element of claim 2, wherein the osmotically active substancecomprises a biocompatible inorganic salt.
 8. The joining element ofclaim 7, wherein the biocompatible inorganic salt is sodium chloride. 9.The joining element of claim 2, wherein the membrane is an elastomermembrane.
 10. The joining element of claim 2, wherein the membrane isfurther configured to regulate the flow of the osmotically activesubstance out of the core.
 11. The joining element of claim 9, furthercomprising an sleeve surrounding at least a portion of the core alongthe longitudinal direction and defining a length in the longitudinaldirection between opposed ends of the outer sleeve, wherein uponexposure of the fluid to the osmotically active substance, theosmotically active substance causes the core to swell against the sleevein the transverse direction and decrease the length of the sleeve withrespect to the longitudinal direction.
 12. A joining element elongatealong a longitudinal direction, the joining element comprising: a corethat extends substantially along the longitudinal direction, the corecomprising a polymer material and an osmotically active substancedistributed in the polymer material; and a sleeve surrounding at least aportion of the core along the longitudinal direction and defining alength in the longitudinal direction between opposed ends of the sleeve,the sleeve comprising at least one thread, wherein the at least onethread defines an angle of intersection with respect to the longitudinaldirection, wherein the osmotically active substance has a variabledistribution density through the polymer material, and the variabledistribution density varies radially with respect to the longitudinaldirection.
 13. The joining element of claim 12, wherein the polymermaterial comprises an elastomer.
 14. The joining element of claim 13,wherein the elastomer comprises a thermoplastic elastomer or across-linked elastomer.
 15. The joining element according to claim 13,wherein the elastomer comprises silicone and the osmotically activesubstance comprises salt crystals.
 16. The joining element of claim 12,wherein the core is configured for controlled release of the osmoticallyactive substance.
 17. The joining element according to claim 13, whereinthe core is extruded.
 18. The joining element of claim 13, furthercomprising a diffusion-limiting membrane surrounding the core, whereinthe membrane is an elastomer membrane.
 19. The joining element of claim12, wherein the sleeve is configured to slide along the core upon afluid expansion of the core such that the at least one angle ofintersection increases.
 20. The joining element of claim 12, wherein theosmotically active substance is disposed in a vesicle within the core.21. The joining element of claim 12, wherein the osmotically activesubstance is dissolved within the polymer material.